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I am looking to build a small circuit board that would allow me to prevent incoming calls from reaching a device but still allow outgoing calls to reach their destination.

This is for a standard RJ11 connector I am looking at working with. I have some experience with small electronics but any pointers on where to get started would be great.

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Can I ask why this was down voted? I believe it is a well formatted question and on topic compared to other questions. – MrStatic Jun 1 '11 at 16:51
are you wanting to actually build a device, as in down to the circuit/pcb level? – Kellenjb Jun 1 '11 at 16:55
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It's off-topic because you haven't actually asked an electrical engineering question. – Leon Heller Jun 1 '11 at 17:08
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If you rephrase it the question it will become on target, this site is a lot about "do it yourself" and your questions is close to "help me find a device". And maybe some info on what country since phone systems is different around the world. (I did not downvote you either) – Johan Jun 1 '11 at 17:08
It would also be helpful to know if this is external analog lines going into these boxes or if they are part of a PBX system. – Joe Jun 1 '11 at 17:25

1 Answer

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You can't prevent incoming calls from reaching the phone, at the phone; that would have to be done at the switching office. You might build something to block it at the phone, but it would be much simpler to incapacitate the ringer. In either case, you'd be unable to an outgoing call (on the same line) while the incoming call was being blocked or trying to ring. The only difference: a blocker might be able to isolate the phone so that picking it up to make an outgoing call while in incoming call was being blocked would get silence. Merely stopping or removing the ringer would still leave the possibility of you inadvertently answering an incoming call.

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